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tty: n_hdlc: get rid of racy n_hdlc.tbuf 

commit 82f2341c94d270421f383641b7cd670e474db56b upstream.

Currently N_HDLC line discipline uses a self-made singly linked list for
data buffers and has n_hdlc.tbuf pointer for buffer retransmitting after
an error.

The commit be10eb7589
("tty: n_hdlc add buffer flushing") introduced racy access to n_hdlc.tbuf.
After tx error concurrent flush_tx_queue() and n_hdlc_send_frames() can put
one data buffer to tx_free_buf_list twice. That causes double free in
n_hdlc_release().

Let's use standard kernel linked list and get rid of n_hdlc.tbuf:
in case of tx error put current data buffer after the head of tx_buf_list.

Signed-off-by: Alexander Popov <alex.popov@linux.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
This commit is contained in:
Alexander Popov 2017-02-28 19:54:40 +03:00 committed by LuK1337
parent 07116057b2
commit 4167230bef
1 changed files with 69 additions and 63 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

132
drivers/tty/n_hdlc.c
View File

@ -114,7 +114,7 @@
#define DEFAULT_TX_BUF_COUNT 3 #define DEFAULT_TX_BUF_COUNT 3
struct n_hdlc_buf { struct n_hdlc_buf {
struct n_hdlc_buf *link; struct list_head list_item;
int count; int count;
char buf[1]; char buf[1];
}; };
@ -122,8 +122,7 @@ struct n_hdlc_buf {
#define N_HDLC_BUF_SIZE (sizeof(struct n_hdlc_buf) + maxframe) #define N_HDLC_BUF_SIZE (sizeof(struct n_hdlc_buf) + maxframe)
struct n_hdlc_buf_list { struct n_hdlc_buf_list {
struct n_hdlc_buf *head; struct list_head list;
struct n_hdlc_buf *tail;
int count; int count;
spinlock_t spinlock; spinlock_t spinlock;
}; };
@ -136,7 +135,6 @@ struct n_hdlc_buf_list {
* @backup_tty - TTY to use if tty gets closed * @backup_tty - TTY to use if tty gets closed
* @tbusy - reentrancy flag for tx wakeup code * @tbusy - reentrancy flag for tx wakeup code
* @woke_up - FIXME: describe this field * @woke_up - FIXME: describe this field
* @tbuf - currently transmitting tx buffer
* @tx_buf_list - list of pending transmit frame buffers * @tx_buf_list - list of pending transmit frame buffers
* @rx_buf_list - list of received frame buffers * @rx_buf_list - list of received frame buffers
* @tx_free_buf_list - list unused transmit frame buffers * @tx_free_buf_list - list unused transmit frame buffers
@ -149,7 +147,6 @@ struct n_hdlc {
struct tty_struct *backup_tty; struct tty_struct *backup_tty;
int tbusy; int tbusy;
int woke_up; int woke_up;
struct n_hdlc_buf *tbuf;
struct n_hdlc_buf_list tx_buf_list; struct n_hdlc_buf_list tx_buf_list;
struct n_hdlc_buf_list rx_buf_list; struct n_hdlc_buf_list rx_buf_list;
struct n_hdlc_buf_list tx_free_buf_list; struct n_hdlc_buf_list tx_free_buf_list;
@ -159,6 +156,8 @@ struct n_hdlc {
/* /*
* HDLC buffer list manipulation functions * HDLC buffer list manipulation functions
*/ */
static void n_hdlc_buf_return(struct n_hdlc_buf_list *buf_list,
struct n_hdlc_buf *buf);
static void n_hdlc_buf_put(struct n_hdlc_buf_list *list, static void n_hdlc_buf_put(struct n_hdlc_buf_list *list,
struct n_hdlc_buf *buf); struct n_hdlc_buf *buf);
static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *list); static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *list);
@ -208,16 +207,9 @@ static void flush_tx_queue(struct tty_struct *tty)
{ {
struct n_hdlc *n_hdlc = tty2n_hdlc(tty); struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
struct n_hdlc_buf *buf; struct n_hdlc_buf *buf;
unsigned long flags;
while ((buf = n_hdlc_buf_get(&n_hdlc->tx_buf_list))) while ((buf = n_hdlc_buf_get(&n_hdlc->tx_buf_list)))
n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, buf); n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, buf);
spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
if (n_hdlc->tbuf) {
n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, n_hdlc->tbuf);
n_hdlc->tbuf = NULL;
}
spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
} }
static struct tty_ldisc_ops n_hdlc_ldisc = { static struct tty_ldisc_ops n_hdlc_ldisc = {
@ -283,7 +275,6 @@ static void n_hdlc_release(struct n_hdlc *n_hdlc)
} else } else
break; break;
} }
kfree(n_hdlc->tbuf);
kfree(n_hdlc); kfree(n_hdlc);
} /* end of n_hdlc_release() */ } /* end of n_hdlc_release() */
@ -402,13 +393,7 @@ static void n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty)
n_hdlc->woke_up = 0; n_hdlc->woke_up = 0;
spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags); spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
/* get current transmit buffer or get new transmit */ tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
/* buffer from list of pending transmit buffers */
tbuf = n_hdlc->tbuf;
if (!tbuf)
tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
while (tbuf) { while (tbuf) {
if (debuglevel >= DEBUG_LEVEL_INFO) if (debuglevel >= DEBUG_LEVEL_INFO)
printk("%s(%d)sending frame %p, count=%d\n", printk("%s(%d)sending frame %p, count=%d\n",
@ -420,7 +405,7 @@ static void n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty)
/* rollback was possible and has been done */ /* rollback was possible and has been done */
if (actual == -ERESTARTSYS) { if (actual == -ERESTARTSYS) {
n_hdlc->tbuf = tbuf; n_hdlc_buf_return(&n_hdlc->tx_buf_list, tbuf);
break; break;
} }
/* if transmit error, throw frame away by */ /* if transmit error, throw frame away by */
@ -435,10 +420,7 @@ static void n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty)
/* free current transmit buffer */ /* free current transmit buffer */
n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, tbuf); n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, tbuf);
/* this tx buffer is done */
n_hdlc->tbuf = NULL;
/* wait up sleeping writers */ /* wait up sleeping writers */
wake_up_interruptible(&tty->write_wait); wake_up_interruptible(&tty->write_wait);
@ -448,10 +430,12 @@ static void n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty)
if (debuglevel >= DEBUG_LEVEL_INFO) if (debuglevel >= DEBUG_LEVEL_INFO)
printk("%s(%d)frame %p pending\n", printk("%s(%d)frame %p pending\n",
__FILE__,__LINE__,tbuf); __FILE__,__LINE__,tbuf);
/* buffer not accepted by driver */ /*
/* set this buffer as pending buffer */ * the buffer was not accepted by driver,
n_hdlc->tbuf = tbuf; * return it back into tx queue
*/
n_hdlc_buf_return(&n_hdlc->tx_buf_list, tbuf);
break; break;
} }
} }
@ -749,7 +733,8 @@ static int n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file,
int error = 0; int error = 0;
int count; int count;
unsigned long flags; unsigned long flags;
struct n_hdlc_buf *buf = NULL;
if (debuglevel >= DEBUG_LEVEL_INFO) if (debuglevel >= DEBUG_LEVEL_INFO)
printk("%s(%d)n_hdlc_tty_ioctl() called %d\n", printk("%s(%d)n_hdlc_tty_ioctl() called %d\n",
__FILE__,__LINE__,cmd); __FILE__,__LINE__,cmd);
@ -763,8 +748,10 @@ static int n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file,
/* report count of read data available */ /* report count of read data available */
/* in next available frame (if any) */ /* in next available frame (if any) */
spin_lock_irqsave(&n_hdlc->rx_buf_list.spinlock,flags); spin_lock_irqsave(&n_hdlc->rx_buf_list.spinlock,flags);
if (n_hdlc->rx_buf_list.head) buf = list_first_entry_or_null(&n_hdlc->rx_buf_list.list,
count = n_hdlc->rx_buf_list.head->count; struct n_hdlc_buf, list_item);
if (buf)
count = buf->count;
else else
count = 0; count = 0;
spin_unlock_irqrestore(&n_hdlc->rx_buf_list.spinlock,flags); spin_unlock_irqrestore(&n_hdlc->rx_buf_list.spinlock,flags);
@ -776,8 +763,10 @@ static int n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file,
count = tty_chars_in_buffer(tty); count = tty_chars_in_buffer(tty);
/* add size of next output frame in queue */ /* add size of next output frame in queue */
spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock,flags); spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock,flags);
if (n_hdlc->tx_buf_list.head) buf = list_first_entry_or_null(&n_hdlc->tx_buf_list.list,
count += n_hdlc->tx_buf_list.head->count; struct n_hdlc_buf, list_item);
if (buf)
count += buf->count;
spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock,flags); spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock,flags);
error = put_user(count, (int __user *)arg); error = put_user(count, (int __user *)arg);
break; break;
@ -825,14 +814,14 @@ static unsigned int n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp,
poll_wait(filp, &tty->write_wait, wait); poll_wait(filp, &tty->write_wait, wait);
/* set bits for operations that won't block */ /* set bits for operations that won't block */
if (n_hdlc->rx_buf_list.head) if (!list_empty(&n_hdlc->rx_buf_list.list))
mask |= POLLIN | POLLRDNORM; /* readable */ mask |= POLLIN | POLLRDNORM; /* readable */
if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
mask |= POLLHUP; mask |= POLLHUP;
if (tty_hung_up_p(filp)) if (tty_hung_up_p(filp))
mask |= POLLHUP; mask |= POLLHUP;
if (!tty_is_writelocked(tty) && if (!tty_is_writelocked(tty) &&
n_hdlc->tx_free_buf_list.head) !list_empty(&n_hdlc->tx_free_buf_list.list))
mask |= POLLOUT | POLLWRNORM; /* writable */ mask |= POLLOUT | POLLWRNORM; /* writable */
} }
return mask; return mask;
@ -858,7 +847,12 @@ static struct n_hdlc *n_hdlc_alloc(void)
spin_lock_init(&n_hdlc->tx_free_buf_list.spinlock); spin_lock_init(&n_hdlc->tx_free_buf_list.spinlock);
spin_lock_init(&n_hdlc->rx_buf_list.spinlock); spin_lock_init(&n_hdlc->rx_buf_list.spinlock);
spin_lock_init(&n_hdlc->tx_buf_list.spinlock); spin_lock_init(&n_hdlc->tx_buf_list.spinlock);
INIT_LIST_HEAD(&n_hdlc->rx_free_buf_list.list);
INIT_LIST_HEAD(&n_hdlc->tx_free_buf_list.list);
INIT_LIST_HEAD(&n_hdlc->rx_buf_list.list);
INIT_LIST_HEAD(&n_hdlc->tx_buf_list.list);
/* allocate free rx buffer list */ /* allocate free rx buffer list */
for(i=0;i<DEFAULT_RX_BUF_COUNT;i++) { for(i=0;i<DEFAULT_RX_BUF_COUNT;i++) {
buf = kmalloc(N_HDLC_BUF_SIZE, GFP_KERNEL); buf = kmalloc(N_HDLC_BUF_SIZE, GFP_KERNEL);
@ -885,54 +879,66 @@ static struct n_hdlc *n_hdlc_alloc(void)
} /* end of n_hdlc_alloc() */ } /* end of n_hdlc_alloc() */
/**
* n_hdlc_buf_return - put the HDLC buffer after the head of the specified list
* @buf_list - pointer to the buffer list
* @buf - pointer to the buffer
*/
static void n_hdlc_buf_return(struct n_hdlc_buf_list *buf_list,
struct n_hdlc_buf *buf)
{
unsigned long flags;
spin_lock_irqsave(&buf_list->spinlock, flags);
list_add(&buf->list_item, &buf_list->list);
buf_list->count++;
spin_unlock_irqrestore(&buf_list->spinlock, flags);
}
/** /**
* n_hdlc_buf_put - add specified HDLC buffer to tail of specified list * n_hdlc_buf_put - add specified HDLC buffer to tail of specified list
* @list - pointer to buffer list * @buf_list - pointer to buffer list
* @buf - pointer to buffer * @buf - pointer to buffer
*/ */
static void n_hdlc_buf_put(struct n_hdlc_buf_list *list, static void n_hdlc_buf_put(struct n_hdlc_buf_list *buf_list,
struct n_hdlc_buf *buf) struct n_hdlc_buf *buf)
{ {
unsigned long flags; unsigned long flags;
spin_lock_irqsave(&list->spinlock,flags);
spin_lock_irqsave(&buf_list->spinlock, flags);
buf->link=NULL;
if (list->tail) list_add_tail(&buf->list_item, &buf_list->list);
list->tail->link = buf; buf_list->count++;
else
list->head = buf; spin_unlock_irqrestore(&buf_list->spinlock, flags);
list->tail = buf;
(list->count)++;
spin_unlock_irqrestore(&list->spinlock,flags);
} /* end of n_hdlc_buf_put() */ } /* end of n_hdlc_buf_put() */
/** /**
* n_hdlc_buf_get - remove and return an HDLC buffer from list * n_hdlc_buf_get - remove and return an HDLC buffer from list
* @list - pointer to HDLC buffer list * @buf_list - pointer to HDLC buffer list
* *
* Remove and return an HDLC buffer from the head of the specified HDLC buffer * Remove and return an HDLC buffer from the head of the specified HDLC buffer
* list. * list.
* Returns a pointer to HDLC buffer if available, otherwise %NULL. * Returns a pointer to HDLC buffer if available, otherwise %NULL.
*/ */
static struct n_hdlc_buf* n_hdlc_buf_get(struct n_hdlc_buf_list *list) static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *buf_list)
{ {
unsigned long flags; unsigned long flags;
struct n_hdlc_buf *buf; struct n_hdlc_buf *buf;
spin_lock_irqsave(&list->spinlock,flags);
spin_lock_irqsave(&buf_list->spinlock, flags);
buf = list->head;
buf = list_first_entry_or_null(&buf_list->list,
struct n_hdlc_buf, list_item);
if (buf) { if (buf) {
list->head = buf->link; list_del(&buf->list_item);
(list->count)--; buf_list->count--;
} }
if (!list->head)
list->tail = NULL; spin_unlock_irqrestore(&buf_list->spinlock, flags);
spin_unlock_irqrestore(&list->spinlock,flags);
return buf; return buf;
} /* end of n_hdlc_buf_get() */ } /* end of n_hdlc_buf_get() */
static char hdlc_banner[] __initdata = static char hdlc_banner[] __initdata =